1. Field of the Invention
The invention concerns a process for the production of high resilience, open celled foams containing urethane groups from polyether polyols, polyisocyanates, water, catalysts, emulsifiers or stabilizers, cross-linking agents and, if necessary, organic blowing agents.
The invention particularly concerns a process for the production of highly flexible polyurethane foams (so-called high-resilience foams) by using, as raw materials, polyether polyols composed exclusively of alkylene oxides and toluylene diisocyanates which are customary in the production of urethane foams.
2. Description of the Prior Art
Flexible polyurethane foams are widely used in the upholstery industry. The object in the development of these foams was to reproduce the physical properties of natural latex foams. Those polyurethane foams which are technically referred to as high resilience polyurethane foams come closest to the physical properties of latex foams. They are characterized in their physical properties, as compared to the conventional flexible polyurethane foams, in that their force-deformation characteristics have no plateau, the quotient of compression hardness at 65 and 25% deformation is over 2.4, and their resilience should be over 50%.
High resilience foams with these properties have already been described in the literature. However, the problems encountered in the production of these foams have greatly limited the amount of this material produced commercially.
Technically, it is desirable to produce the foams in continuous blocks or in molds according to the so-called "one shot method". Such foams should not sag or shrink after rising in the curing stage. In order to achieve this goal, it is necessary that the cells of such foams at least partly open after rising without mechanical action. This can be frequently recognized by the fact that the foams blow off. Additionally, it is desirable that foams can be produced according to a given process with a wide variability in their density, for example, slabstock foams with densities between 18 and 50 kg/cu m and molded foams with densities between 30 and 80 kg/cu m.
Attempts to produce such high resilience polyurethane foams in these density ranges with conventional polyols and toluylene diisocyanates in a manner such that their cell windows open after rising, have been only partly successful. Most of the methods suggested for the production of high resilience foams have the disadvantage that the cell windows of the foams do not open or open insufficiently after rising so that the foams shrink after curing. The shrinkage can be avoided by compressing the foams shortly after rising, so that the cell walls of the foams are mechanically ruptured. This procedure has serious drawbacks, particularly, in the case of low densities, since the physical properties of the foams are substantially impaired by tearing in the incompletely cured state.
Foams with the desired properties according to the state of the art have been successfully prepared by modifying the raw materials required for foaming.
Thus, for example, it is known from DOS No. 2,242,476 and U.S. Pat. No. 3,383,351 to use modified polyether polyols which contain grafted organic polymeric side chains instead of the conventional polyether polyols. These side chains can be obtained by radically induced grafting of styrene and/or acrylonitrile. A detailed description of this procedure is found in the above mentioned DOS No. 2,242,476.
Another solution is disclosed in DOS No. 2,221,811 and DOS No. 2,232,525. According to these patents, modified isocyanate components are used which are essentially isocyanates containing isocyanuric acid rings or biuret, allophanate- and/or urethane groups.
The use of special modified polyether polyols or modified isocyanates necessarily leads to an increase in the cost of the product. For the foam manufacturer, it is still desirable, in practice, to produce high-resilience polyurethane foams from conventional polyether polyols, that is, polyether polyols composed exclusively of alkylene oxides, and diisocyanates, which are available to the processor as the most economical raw materials for the production of polyurethane foams.